Process for preparing crystals of chrome alum



Patented July 22, 19241.

()FFICEo raoonss son PREPARING oRYs'rAns or cimomn AL-UM.

No' Drawing.

To all whom it may concern:

Be it known that I, PETER HASENCLEVER, a citizen of Germany,'residing at 29 Billbrookdeich, Hamburg-Billwarder, Germany, have invented certain new and useful Improvement in Processes for Preparing Crystals of Chrome Alum, of which the following is a specification.

The present invention refers to crystals of chrome alum.

It is known to manufacture chrome alum by mixing solutionsof chromium sulphate with potassium sulphate. It is necessary that the said solutions stand for a longer time, as for several weeks in order that the so called green modification which is unpreparing crystallizable may turninto the violet modification of chrome alum which is crystallizable. For accelerating this transformation one has proposed to add to the solution of chrome alum nitric acid, sulphurous acid or sulphites.

The present process consists in that one adds to the solutions of green chrome alum potassium dichromate, sulphurous acid and sulphites. The green modification of chorme alum. turns nearly at once into the violet modification at low temperature so that at suitable tem erature and concentration the crystals of c rome alum are formed at once such amounts of dichromates that the fer-1 rous com ounds' are not oxidized to ferric compoun s. If however the ferrous compounds should be oxidlzedto ferric compounds the sulphurous acid will effect a reduction. The sulphurous acid may be introduced into the solution while or after the addition of potassium dichromate and sulphuric acid. The amount of the sulphurlc acid is suitably so taken that it may form Application filed November 11, 1922. Serial No. 0,451.

with the whole amount of potassium in the potassium bichromate, potassium sulphate.

An explanation of the present process cannot be given. Probably from the potassium dichromate in the presence of the sulphuric acid by the action of sulphurous acid at once violet chrome alum is formed which in statu nascendi transforms at once the green chrome alum into the violet modification.

In the vcase that the solutions contain ferrous compounds the latter remain in solution in larger proportion than if one adds 1000 kilograms ferrochromium, preferably in large lumps or blocks asthe material comes from the manufacturer, are dissolved in about 3000 kilograms concentrated sulphuric acid, so that the sulphuric acid is nearly completely neutralized. One may subject the solution consisting of chromium sulphate and ferrous sulphate to a crystal lization process in order to remove a part of the ferrous sulphate, about one half. The liquid may be separated from the crys-'' tals for instance by centrifuging and is now treated with potassium. sulphate, in such proportions that the whole amount of chromium sulphate may be transformed into chrome alum. The addition is preferably made while the solution is hot, whereupon the liquid is cooled and then treated with about 1O kilograms potassium dichromate and about 3 kilo ams concentrated sulphuric acid. Sulp urous acid is then introduced into the li uid. The conversion of the green modificatlon of the chrome alum into the violet modification may be soon obmow-use ohiome alum which consists in adding pophurous acid to solutions or chrome alum tassium dichromate, sulphuric mid and sulprepared by dissolving ierrochromium in phurous acid I130 solutions of chrome alum sulphuric acid, to which has been arided poand crystullizing tassium sulphate, and crystallizing. 5 2. The process for preparing crystals of In testimony whereof K hereunto affix my chrome alum which conslsts in adding posignature.

tassiuui dichromate, sulphuric acid. and sull- FETER HASENCLEVER. 

